The present invention relates to a cutting knife for a cutting tool for cutting through adhesive beads on glass panes in particular on vehicles, having a cross section that is bent into a U-shape and comprises a first limb with a receiving opening for attachment to an oscillating drive, and a second limb that is configured as the cutting part and is joined via an intermediate part to the first limb of the cutting knife, the intermediate part and the second limb being shaped such that a distance exists in the radial direction between the center point of the receiving opening and at least one cutting edge.
Cutting knives of this kind bent into a U-shape are known, for example, from German patent 3,324,676 and from U.S. Pat. No. 4,543,720: the former discloses a cutting part, curved in a sickle shape, that faces away from the receiving opening; and the latter discloses a cutting part, curved in a sickle shape, that faces toward the receiving opening. Also known from U.S. Pat. No. 4,980,976 is a cutting knife, bent into a U-shape, whose cutting part is straight.
A characteristic shared by the known cutting knives is that when cutting through adhesive beads, for example to remove a damaged motor vehicle windshield, there is a considerable risk of breakage for the cutting knife.
The reason for this is on the one hand the tough material of the adhesive bead, usually made of a specific type of polyurethane, and on the other hand the energy expenditurexe2x80x94which in some cases can be quite substantial despite the drive system that oscillates at high frequency and with a small pivot anglexe2x80x94especially when cutting through wider adhesive beads, such as often occur in particular in the case of windshields that have already been replaced once, so that the adhesive bead had to be applied manually when installing the windshield.
An increased risk of breakage exists in particular in the case of cutting knives that, because of the geometry of the motor vehicle in question, must have a relatively long cutting part; this is also specifically the case for a cutting knife having a straight cutting part, as defined in U.S. Pat. No. 4,980,976, which makes possible particularly long straight cutting parts.
It is therefore an object of the invention to improve a cutting knife of the kind cited initially in such a way that the susceptibility to breakage is reduced. It is a further object of the invention to disclose a cutting knife which allows to reduce the energy expenditure necessary for cutting through an adhesive bead.
According to the present invention these and other objects are achieved, in the case of a cutting knife of the kind cited initially, in that the second limb has, in a middle region between its outer free end and its angled transition to the intermediate part, a smaller width than at the transition and at the outer end.
The object of the invention is completely achieved in this fashion.
Specifically, it was recognized in the course of the invention that in the previously known cutting knives, the risk of breakage is greatest at the transition from the cutting part to the intermediate part. On the other hand, the risk of breakage cannot be eliminated simply by widening the cutting part at the transition to the intermediate part. The reason is that too wide a cutting part results in greatly increased friction between the cutting part and the portion of the adhesive bead that has already been cut through, and thus in a greatly increased energy expenditure when working.
With the configuration of the cutting knife according to the present invention, on the one hand the risk of breakage is improved because of the enhanced stability due to the widening of the cutting part at its transition to the intermediate part; the subsequent constriction of the cutting part toward the outside reduces the force necessary to cut through the adhesive bead. In addition, the fact that the cutting part widens again toward its outer end results in greatly improved centering of the cutting part during the cutting operation, which yields not only better guidance but also reduced energy expenditure.
What is moreover taken advantage of here is the fact that because of the specific geometry between the vehicle""s glass pane and body flange, a certain distance usually exists, while working, between the spacing plate and the adhesive bead being cut through, so that a wider configuration of the cutting part at its end facing toward the spacing plate results in almost no increase in energy expenditure.
According to a development of the invention, the cutting part has a first cutting edge that faces toward the receiving opening and is concavely curved with respect thereto, and a second cutting edge that faces away from the receiving opening and is convexly curved with respect thereto.
This feature makes possible improved centering and guidance of the cutting knife while working, both when the cutting knife is pulled toward the receiving opening while working, and also when the cutting knife needs to be guided back in an opposite direction in the portion of the adhesive bead that has already been cut through.
According to the further embodiment of the invention, the cutting part has a first cutting edge that faces toward the receiving opening and is concavely curved with respect thereto, and a second cutting edge that is straight or slightly convexly curved and faces away from the receiving opening.
An embodiment of this kind is advantageous particularly if work is to be performed with the cutting knife only in one preferred direction, namely toward the receiving opening. Stability is further improved by the fact that the cutting part is then somewhat wider overall.
According to a further feature of the invention, the cutting part has a first cutting edge that faces toward the receiving opening and is straight or is slightly convexly curved, and a second cutting edge that faces away from the receiving opening and is convexly curved with respect thereto.
This kind of embodiment of the cutting knife is advantageous in particular when, because of the particular geometry on certain motor vehicles, the principal working direction does not, as in the case of the two embodiments cited above, extend from the cutting part toward the receiving opening, (i.e. the knife is not, so to speak, pulled through the adhesive bead), but rather the cutting knife must be guided in the opposite direction, i.e. in a manner of speaking must be pushed through the adhesive bead. Because the cutting edge is then concavely curved toward the advance direction, the cutting operation is in turn facilitated by the scything effect, while the susceptibility to breakage is reduced by the overall somewhat wider configuration of the entire cutting part.
According to a further feature of the invention, the cutting part has a tip at its outer end.
This feature makes it easier to insert the cutting part through the adhesive bead.
According to a further feature of the invention, the cutting part is shaped so that the radial distance to the center point of the receiving opening increases from the transition out toward the outer end.
This geometry, which in other words moves the cutting part farther toward the outer end away from the center point of the receiving opening, results in greater deflection of the cutting part by the linear stroke of the oscillating drive itself. This reduces the muscle force to be applied by the user when cutting through an adhesive bead, since the linear stroke of the oscillating drive itself is utilized to a greater extent.
It is understood that the features of the invention mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the context of the invention.